Recent promising human results of immunotherapies to block immune checkpoints such as cytotoxic T-lymphocyte-associated antigen 4 (CTLA4) and programmed cell death protein 1 (PD-1) (Pardoll, D. M., Nat Rev Cancer 12:252-264 (2012); Pardoll, D. M., Nat Immunol 13:1129-1132 (2012); Keir, M. E. et al., Annu Rev Immunol 26:677-704 (2008)) illustrate the importance of targeting molecules that inhibit T cell-mediated antitumor immunity. However, the immunosuppressive tumor microenvironment hampers the success of various immunotherapies. There are several intracellular checkpoints with great potential as targets to promote potent antitumor immunity. STAT3, for example, has been shown to be a crucial signaling mediator in tumor-associated immune cells, as well as in tumor cells (Yu, H. et al., Nat Rev Cancer 9:798-809 (2009); Kortylewski, M. and Yu, H., Curr Opin Immunol 20:228-233 (2008); Kortylewski, M. et al., Nat Med 11:1314-1321 (2005); Herrmann, A. et al., Cancer Res 70:7455-7464 (2010)). In tumor cells, STAT3 promotes tumor cell survival/proliferation, invasion, and immunosuppression (Yu, H., and Jove, R., Nat Rev Cancer 4:97-105 (2004)). In the tumor microenvironment, STAT3 is persistently activated in immune cells, including T cells (Kujawski, M. et al., Cancer Res 70:9599-9610 (2010); Yu, H. et al., Nat Rev Immunol 7:41-51 (2007)). CD4+ T regulatory cells (TRegs) can induce peripheral tolerance, suppressing CD8 T cell functions in various diseases including cancer (Kortylewski, M. et al., Nat Med 11:1314-1321 (2005); Curiel, T. J. et al., Nat Med 10:942-949 (2004); Shevach, E. M., Nat Rev Immunol 2:389-400 (2002); Chen, M. L. et al., Proc Natl Acad Sci USA 102:419-424 (2005); Mempel, T. R. et al., Immunity 25:129-141 (2006); Arens, R. and Schoenberger, S. P., Immunol Rev 235:190-205 (2010)). Activated STAT3 in T cells contributes to expanding tumor-associated CD4+ TRegs (Kortylewski, M. et al., Nat Med 11:1314-1321 (2005); Pallandre, J. R. et al., J Immunol 179:7593-7604 (2007)). Moreover, Stat3−/− CD8+ T cells, both endogenous or adoptively transferred, mount potent antitumor immune responses compared to those with intact Stat3 (Kujawski, M. et al., Cancer Res 70:9599-9610 (2010)).
As a nuclear transcription factor lacking its own enzymatic activity, STAT3 is a challenging target for both antibody and small-molecule drugs (Yu, H., and Jove, R., Nat Rev Cancer 4:97-105 (2004); Darnell, J. E., Nat Med 11:595-596 (2005); Darnell, J. E., Jr., Nat Rev Cancer 2:740-749 (2002)). Recent pioneering work has shown the feasibility to deliver siRNA into tumor cells in vivo (McNamara, J. O., 2nd et al., Nat Biotechnol 24:1005-1015 (2006)). In particular, chimeric RNAs or DNA-RNAs consisting of a siRNA fused to nucleic acid sequences, which bind to either a cell surface ligand or an intracellular receptor with high affinity, have demonstrated therapeutic efficacy in preclinical models (McNamara, J. O., 2nd et al., Nat Biotechnol 24:1005-1015 (2006); Wheeler, L. A. et al., J Clin Invest 121:2401-2412 (2011); Kortylewski, M. et al., Nat Biotechnol 27:925-932 (2009)). The majority of such siRNA delivery technologies involves the fusion of siRNA to an aptamer, a structured RNA with high affinity to epitopes on tumor cells and virally infected epithelial cells. Applicants recently described a technology for efficient in vivo delivery of siRNA into immune cells by linking an siRNA to CpG oligonucleotide, which binds to its cognate receptor, TLR9 (Kortylewski, M. et al., Nat Biotechnol 27:925-932 (2009)). TLR9 is expressed intracellularly in cells of myeloid lineage and B cells, as well as tumor cells expressing TLR9, including human leukemic cells (Kortylewski, M. et al., Nat Biotechnol 27:925-932 (2009); Zhang, Q. et al., Blood 121:1304-1315 (2013)). However, the CpG-siRNA approach does not directly target T cells (Kortylewski, M. et al., Nat Biotechnol 27:925-932 (2009)).
Recently, an effective way to deliver siRNA into CD4 T cells for local treatment of HIV has been developed (Wheeler, L. A. et al., J Clin Invest 121:2401-2412 (2011)). However, for cancer immunotherapy, it is also crucial to regulate CD8+ effector T cells, in addition to CD4+ cells. Further, it is quite plausible that selectively targeting the subpopulations of CD8+ and CD4+ T cells in the tumor microenvironment, rather than T cells in general, should afford more antitumor efficacy while reducing toxicity. The expression of CTLA4 is dysregulated in tumors and in tumor-associated T cells and is a promising immunotherapeutic target (Santulli-Marotto, S. et al., Cancer Res 63:7483-7489 (2003)). The broad antitumor immune response by CTLA4 blockade is thought to be mainly mediated by CD4+ T cells: reducing TRegs and increasing helper T cells (Chen, M. L. et al., Proc Natl Acad Sci USA 102:419-424 (2005); Wing, K. et al., Science 322:271-275 (2008); Byrne, W. L. et al., Cancer Res 71:6915-6920 (2011); Peggs, K. S. et al., J Exp Med 206:1717-1725 (2009); Lenschow, D. J. et al., Annu Rev Immunol 14:233-258 (1996)). However, activated/exhausted CD8 T cells also express CTLA4 (Walunas, T. L. et al., Immunity 1:405-413 (1994); Teft, W. A. et al., Annu Rev Immunol 24:65-97 (2006); Wherry, E. J. et al., Immunity 27:670-684 (2007)).
There is a need in the art for compositions and methods of delivering modulators of cell activity (e.g., anti-tumor agents, anti-obesity agents) to cells (e.g., malignant cells, tumor-associated T cells, effector T cells) to inhibit diseases such as cancer, metastasis or metabolic diseases. The nucleic acid compounds and methods of using the same as provided herein cure these and other needs in the art.